There are only three groups of people who really think it's supposed to be necessary to buy the new and improved version of a camera every year:

Camera manufacturers.

Electronics retailers.

People who frequent camera forums.

It's not necessary. The gains from year to year are almost always marginal. Only very rarely, such as with the E-M5 or the D800, is it not marginal. The rest of the time, you can keep going with the same model of camera for a while longer.

We are getting to the point of the last camera we need. Sure, sensor technology will continue to be refined, better and better cameras will to come out, but we're getting a lot of diminishing returns: How many of us REALLY need to photograph black cats on coal piles by the light of the new moon? I haven't had any great compulsion to upgrade from my GH2/E-PL1, because I know the technical limitations of what I do.